You don't say how slowly you are weaning off. If you are wanting to wean off cortef you need to do it slowly. Even as slow as a mg a week. Play around with with your dosage so you don't feel the reduction.
You also don't mention why you want to come off the cortef. If you are feeling healing healthy at 30 mg maybe thats what you need. A good yahoo group for cortef is nthadrenals